Although in principle applicable to any micromechanical sound transducer system, for example loudspeakers and microphones, the present invention and the problem on which it is based are explained with reference to micromechanical microphone systems on silicon basis.
Micromechanical microphone systems may have a sound transducer device integrated on a MEMS chip for converting sound energy into electrical energy, a first electrode deflectable by sound energy and a fixed, perforated second electrode interacting capacitively. The deflection of the first electrode is determined by the difference of the sound pressures in front of and behind the first electrode. If the deflection changes, then the capacitance of the capacitor formed by the first and the second electrode is modified, which measuring technology is able to detect.
Ribbon microphones are believed to have been understood for some time. They function according to an inductive functional principle, the deflection of a diaphragm resulting in a modification of a magnetic flux through a coil configuration, which in turn induces a voltage in the coil configuration.
Because of the induction of a current corresponding to the induced voltage, it is not necessary to generate and regulate a high operating voltage of the capacitive operating principle, which result in a substantial reduction of the power consumption and a cost reduction because of the omission of high-voltage-generating circuit parts.
This yields numerous advantages compared to the capacitive operating principle. Thus it is possible to implement a directional dependency of the ribbon microphone since it is possible to operate it as a differential-pressure microphone. Due to its small power consumption, the inductive principle allows for an always-on and wake-up functionality. The sensitivity scales with the length and number of the ribbons and not, as in the capacitive principle, with the deflection surface. Capacitive MEMS microphones therefore cannot be scaled down without performance losses. Furthermore, there is an increased mechanical robustness due to the low mass of the oscillatory material.
Ribbon microphones are discussed in U.S. Pat. No. 6,434,252 B1 and WO 2006/047048 A2, in which a ribbon located in a magnetic field is excited to oscillate by sound waves, which induces a voltage in the ribbon.
U.S. Pat. No. 8,031,889 B2 discusses a miniaturized ribbon microphone, which has a low sensitivity since the coils are configured in one plane and a voltage is induced only by deflection components in the vertical direction.